using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    { 

        var stringToTest="email@gmail.com";

        var stringtoTest2= "NotAValid@h.com";

        string pattern = null;

        pattern = "^([0-9a-zA-Z]([-\\.\\w]*[0-9a-zA-Z])*@([0-9a-zA-Z][-\\w]*[0-9a-zA-Z]\\.)+[a-zA-Z]{2,9})$";

        //check first string

       if (Regex.IsMatch(stringToTest , pattern))

       {          

            Console.WriteLine(stringToTest+ " is Valid Email address ");

       }

       else

       {

            Console.WriteLine(stringToTest + " is Not a Valid Email address");          

       }

​

        //check second string

       if (Regex.IsMatch(stringtoTest2 , pattern))

       {          

            Console.WriteLine(stringtoTest2+ " is Valid Email address ");

       }

       else

       {

            Console.WriteLine(stringtoTest2 + " is Not a Valid Email address");         

       }

    }

}